Before I matched the lower with the upper, I used my lower with my friend's Daniel Defense mid-length upper with the ST-T2. We were using federal brass 5.56 ammo. Everything worked perfectly.

Forward to this past Saturday:

Got my YHM upper and headed to the range. I wasn't too concerned about anything really except to see if the AR worked with Tula/WPA.

I had one 30-round magazine (PMAG) loaded with Tula and had 2 PMAGs loaded with PMC.

I fired all rounds of the Tula without fail. It worked perfectly. I then loaded the mag with brass. Fired one shot successfully and the second round failed to feed. Ejected the round and tried again. Same result.

I have heard of an AR-15 having issues firing steel-cased but I seem to be having the opposite issue.

Is this from the ST-T3 not being right for the mid-length gas system on my YHM upper?

Load one round in mag and fire it and see if the bolt locks back on empty mag. Buffer is probably too heavy. Standard weight carbine buffer should work fine. If it will not lock back on empty mag then it is possibly short stroking due to too heavy a buffer.

Anything I build I always start with the standard weight buffer and usually that is all that is needed. If everything is working and brass is ejecting between 3 and 4 o'clock then leave it. If you need to adjust the weight to get the ejection pattern right then go with T2.

Hey mobuck, good point. My other AR used the ST-T2 buffer and functioned perfectly with brass or russian. I was at the store when building the lower and they only had the ST-T3. The guy said it wouldn't make a difference. I guess he was wrong.

I performed the test 10 times that HOW CTS (slappy?) suggested and the bolt locked back only 20% of the time. Indicated likely buffer is too heavy. I haven't had the chance yet to test a standard buffer and to use my upper on my friend's lower with the ST-T2 that functions perfectly in his AR. Those tests should tell me what I need to know. I'll be running those tests this coming weekend.

Forgot to mention with the AR stripped and thoroughly cleaned, when at the range testing with one round in the mag per HOW CTS recommendation, I decided to test multiple rounds again with Tula. This time, the failures also happened with the Tula 223 rounds the same way as it did before with the PMC.

Yea I changed my screen name and there was a slight mix up. It's straightened out now. I am not saying that a heavier buffer is never the answer. What I was saying is that I never start out with a heavy buffer. The standard buffer is what most normally run on and maybe I have been lucky but that is all I have ever had to use. If you have ejection problems then go from standard to the next heavier and see if that solves it. In your case, I would try the next lighter and see what happens or even go back to a standard carbine buffer and see if that solves the problem. Another thing to check since you say the bolt locked back 20% of the time would be to see if the bolt actually locked back on the bolt catch itself as it should or as sometime will happen when short stroking, the bolt catch will catch the front edge of the carrier, which would still indicate that the BCG is not moving back far enough.

Forgot to mention with the AR stripped and thoroughly cleaned, when at the range testing with one round in the mag per HOW CTS recommendation, I decided to test multiple rounds again with Tula. This time, the failures also happened with the Tula 223 rounds the same way as it did before with the PMC.

What failures are you having? Is the bolt not locking back after the last round each time?

I always suggest eliminating a few factors when people have issues with their AR15 by using reliable magazines and ammo:

First, use reliable mags like Pmags. So if you know your mags (pmag/gi) is working fine, then its not a mag issue.

Second, use the same ammo for each test, starting with factory brass ammo only and see if you are still having the issues.

If you know your mags and ammo are good and not the source of the problem, then you can start isolating the gun. In your case it might be the buffer you are using. If its too heavy of a buffer, that will cause it to short stroke and not lock back/feed the next round.

Using the method CTS described (1 round in mag test), is the rifle locking back after the shot or not?

----

Try this:
use standard 5.56NATO ammo only, preferrably Federal M193 or M855 with Pmags. Do the one round test a few times to see if its locking back after the last round.

So are you having problems with the bullets feeding from the magazine, or not chambering? The reason I ask is you said you "ejected the round". Which means it fed fine, but did not chamber. Which (generally) means it's not the magazine, but the chamber. If it was the magazine you'd of said something like "double feeds" or "round jams itself over the gas tube". Steel case doesn't expand like brass, so it doesn't seal the gasses as well, fouling the chamber more than normal. Not to mention that laquer crap on tula ammo doesn't burn, and the powder it turns into fouls the chamber as well. Is your rifle a 5.56 nato, .223, or wylde chamber? Depending on which one it could be a bit tighter specs. Couple that with a fouled chamber and you could have failure to chamber issues. Also there could've been something on your magazine which could've got jammed in your star chamber. When I was a dumb private on a ftx I dropped some foam earplugs in an empty magazine pouch. Some time later I shoved 2 mags loaded with blanks upside down in that pouch. Needless to say, at the thickest part of out engagement I'm having serious chambering issues and trying to dig burnt pieces of foam earplug out of my star chamber. Not saying you have earplugs in there, but if there's a lot of built up crap it can keep your bolt from fully seating causing issues.

Usually if you go from steel to brass you have failure to extract issues, as the brass will feed and chamber, but when it expands it gets stuck. Going from steel to brass is generally a bad idea without a good chamber cleaning. I suppose you could have a failure to chamber if you had a tight spec's chamber that got dirty... I use a nitrided barrel with a wylde chamber and have yet to hit these issues, and I'm fairly liberal with my cleaning regime...

I think it is pretty simple really. He is using an H3 (T3) buffer in a standard 1:9 twst carbine shooting factory ammo. It is short stroking due to having too heavy a buffer. If the buffer is too heavy the bcg cannot overcome the added weight so it will not retract back far enough into the stock to pick up the next round or to lock open on an empty mag.

Exactly my point. Failed to FEED. I.E. was never stripped from the magazine. How do you eject a round that was never stripped from the magazine? Which was why I was trying to get a common language so we knew the real problem. Hence the functions of the rifle.

If a rifle fails to feed, nothing is chambered, nothing can be ejected. HOWEVER if a round failed to CHAMBER it can be ejected. Get my drift? You're giving solutions to something that may not be the problem, because he's describing (potentially) the wrong symptoms.

If a rifle FAILED TO FEED why would you cycle it just to EJECT the bullet that never fed?

__________________
Freedom's just a word. If I'm gonna die for a word, my word is jello...

I think he may just not be saying it quite right. I believe he means that he is either having to pull the charging handle to the rear to charge the next round or, the bolt is catching the case just forward of the rim and starting to strip it partially out of the mag before finally slipping off leaving the bolt jammed against the partially chambered round. I have seen that happen quite a bit. At any rate, an T3 buffer is way too heavy for a standard carbine shooting factory loads. Especially one with mid length gas. It may be ok if it were heavy target loads that were loaded to near max charges and carbine gas which is usually way overgassed anyway.

I may be wrong, I just know that I have run into many problems because people think a heavy buffer is going to makes something better. Basically trying to fix a problem that didn't exist. I hope it didn't seem like I was getting on your case. It would help if they made a sticky or something that described the different issues and what they mean like FTF, FTE, etc.
I have even had people bring their rifle to me with a heavy buffer and when you ask them why they changed it they say something like, I read on the internet that it was better. No problem to start with, just wanted something better. Something better causes a problem then they are looking for a gunsmith.

Get people on the internet to agree to one thing? (set of rules for names and ways of describing malfunctions in this case)

HAHAHA! That will surely be a smooth and beautiful process...

As for my issue, I am actually surprised that I may need to use an H2 buffer. Seems heavy for a mid gas to me. Maybe the gas port is oversized to prevent issues with people building these things and just slapping in an H2 buffer off the bat, thinking it is better, but is in fact usually not good for a mid.

My further reading has lead me to believe that PSA uppers are slightly over gassed.

Probably by choice... They are cheaper than some places while still maintaining a good quality product. (in their "premium" line at least) This has led to them being popular... and they get a lot of new to AR builders because of this as well. Combine less experienced users with an internet talking up the virtues of heavier buffers, and they probably had a lot of calls about guns malfunctioning (short stroking) and that caused CS issues. This would be exacerbated in the Mid gas guns if the owners had no clue the differences.

Over gas the system a little to make up for owners tendencies to over buffer, and the problem goes away.

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